Self-regulated resonating apparatus



United States Patent O York Filed Feb. 6, 1967, Ser. No. 614,295 Int. Cl. B02c 17/24; B01f 9/02, 11/00 US. Cl. 24136 10 Claims ABSTRACT OF THE DISCLOSURE A resonant dispersion system for fluid materials including two spaced masses having tubes through which the fluid passes and connected by springs and by a hydraulic piston and cylinder. The masses are mounted on flexible supports to permit opposed oscillatory motion and a transformer having a movable core connected between the masses detects the frequency and phase of oscillation. A feedback circuit, responsive to signals from the transformer, controls application of hydraulic fluid to the piston and cylinder so as to assure synchronism of the driving force with the resonant frequency of the system.

BACKGROUND OF THE INVENTION This invention relates to resonating apparatus and, more particularly, to a new and improved mechanical resonating apparatus which maintains synchronism regardless of variations in the resonant frequency of the apparatus.

In one method of continuous grinding or milling of fluid material containing particles to be ground or dispersed, the material is directed through an array of parallel tubes containing metal balls or other grinding particles and the tube array is vibrated in a direction perpendicular to the length of the tubes. Preferably, the tube array is included in a spring system and the vibrations are imparted at the resonant frequency of the system, thereby reducing the power which must be applied in order to maintain oscillation. Often, however, the mass of the fluid material passing through the tubes changes appreciably during the operation of the apparatus, resulting in a corresponding change in the resonant frequency of the system. With such changes in resonant frequency, perfect synchronism between the driving piston and the oscillating tube array is lost, thereby increasing substantially the required driving power.

Accordingly, it is an object of the present invention to provide a new and improved resonating apparatus which overcomes the above-mentioned disadvantages of present resonating apparatus.

Another object of the invention is to provide a resonating apparatus capable of maintaining synchronism despite changes in the oscillating mass of the apparatus.

SUMMARY OF THE INVENTION These and other objects of the invention are attained by providing, in a resonant system including an oscillating member and a driving element for imparting motion to the oscillating member, a control unit for controlling the frequency of oscillation of the driving element and a feedback circuit responsive to oscillatory motion of the member for regulating the operation of the control unit in accordance with signals from the feedback circuit. In one embodiment of the invention a linear velocity differential transformer detects the frequency and phase of oscillation of the oscillating member and supplies a signal to an amplifier which in turn controls the application of hydraulic fluid to a driving piston and cylinder so as to maintain oscillation at the resonant frequency 3,5fi2,273 Patented Mar. 24, 1970 of the system. In addition, a starting unit providing output signals in synchronism with signals from the transformer is adapted to be connected to the amplifier to initiate and maintain oscillation under low gain conditions.

BRIEF DESCRIPTION OF THE DRAWING The single figure of the accompanying drawing illustrates, partially in block diagram form, a representative self-regulated resonating apparatus according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the typical resonating system shown in the drawing, two adjacent steel masses 10 and 11 are each supported from a base or floor 12 by four legs 13 which are sufliciently resilient to permit oscillatory motion of the masses in the direction toward and away from each other. Two coil springs 14 and 15 extending between the masses provide a resilient connection, so that the oscillatory system comprising the masses 10 and 11, the supports 13 and the springs 14 and 15 has a resonant frequency of oscillation. Preferably, the size of the masses and the spring constants of the supports 13 and springs 14 and 15 are selected so as to provide a resonant frequency within the range from about 20 c.p.s. to about 60 c.p.s.

In order to supply driving power to the masses to maintain oscillatory motion, they are joined by a hydraulic piston 16 and cylinder 17 connected through a control valve 18 mounted on the cylinder and through a high pressure conduit 19 to a hydraulic power unit 20 supported on the base 12. The piston 16 and cylinder 17 may be of any conventional type adapted to impart oscillatory motion as, for example, the Vickers two inch diameter by two inch stroke piston and cylinder utilizing a clevis mount available from the Vickers Incorporated, Division of Sperry Rand Corporation, Troy, Mich. Similarly, the valve 18 may be of a conventional type adapted to provide instantaneous response to electrical signals such as the Vickers SD4-06 Servo-Valve and the hydraulic power unit 20 may be a conventional 10 to 15 horsepower unit operating at 1000- p.s.i., for example.

Each of the steel masses 10 and 11 is provided with an array of tubes 21 in which a large number of small grinding particles (not shown), such as carbon steel balls or other hard elements, is held captive in accordance with conventional continuous grinding mill practice. In addition, two flexible conduits 22 and 23 are connected to a end plate 24 on each of the steel masses to supply fluid having particles to be ground and to remove the processed fluid, respectively. Behind each of the end plates the tubes 21 of the mass may be connected either in series or in parallel, or in a series-parallel arrangement, depending upon the needs of the particular grinding process.

In accordance with the invention, the amplitude, frequency, and phase of oscillation of the masses 10 and 11 are detected by a linear velocity differential transformer 27 mounted on the mass 10. The transformer 27 contains a coil array 28 into which a core member 29 affixed to the other mass 11 is partially received. As the masses 10 and 11 move toward and away from each other, the reactance of the transformer coil array 28 is varied by the change in position of the core member 29. This provides an output signal on a line 30 which accurately represents the frequency and phase of oscillation of the 3 the line 30. The phase shifter 31 may include, for example, a reactive element connected in series with the control element 33, and also a reversing switch. In this way, the phase of the detected signal may be matched to that of the driving power applied to the cylinder 17 by the valve 18.

From the phase shifter, the signal representing the frequency and phase of oscillation is applied by a line 34 to a start generator 35 and also to a summing amplifier 36 which may be of any conventional construction. This amplifier increases the amplitude of the signal from the line 34 in accordance with the setting of a control resis- 1tor 37 in a gain control unit 38 and transmits the amplified signal on a line 39 to the hydraulic control valve 18 so as to control the application of hydraulic fluid to the piston 17. By varying the setting of the gain control resistor 37, the amplitude of the oscillations of the masses may be regulated.

Because the operation of the system is dependent upon the magnitude of the feedback signal and the amplification thereof, oscillation will not be maintained if the overall gain of the feedback loop is less than unity. Consequently, where low amplitude operation is desired, the start generator 35 is utilized. This generator comprises a self-excited oscillator having a frequency close to the resonant frequency of the spring and mass system and providing an output adapted to be connected through a switch 40 to the summing amplifier 36. Inasmuch as the feedback signal from the line 34 is connected to the generator 35, the oscillator therein automatically locks in to both the frequency and the phase of the feedback signal, so that when the generator output is added to the feedback signal in the amplifier 36, there is provided an output signal of sufiicient magnitude to maintain oscillation at low amplitude. Moreover, when the gain control unit 38 is adjusted to provide an overall feedback circuit gain greater than unity, the start generator is automatically biased to inoperative condition by a signal on a line 41.

In operation, a fluid such as paint, containing material such as a pigment to be ground into fine particles, is applied to the input conduits 22 for the masses and 11, so as to be conducted through the tubes 21 of the masses, after which it emerges through the conduits 23. With the hydraulic power unit supplying hydraulic fluid to the valve 18 through the conduit 19, the switch 40 is closed, causing the signal from the start generator 35 to be applied to the amplifier 36. The amplifier signal, applied through the line 39 to the valve 18, causes hydraulic fluid to be transmitted to the piston 16 and cylinder 17, so as to induce oscillation therein and cause the masses 10 and 11 to oscillate at their resonant frequency. The signal from transformer 27, representing this frequency by the shifter 31, is applied after phase correction through the feedback loop to the start generator 35 and to the summing amplifier 36. The amplifier output signal, applied through the line 39 along with the start generator signal if necessary, is sufiicient to maintain oscillation of the masses 10 and 11.

When the mass of the fluid material within the tubes 21 changes as a result, for example, of a variation in the composition of the fluid being processed, the resonant frequency of the oscillating system comprising the masses 10 and 11, the supports 13 and the springs 14 and 15, is changed. In the absence of any feedback control, the valve 18 would continue to supply hydraulic fluid at the original frequency and, because of the lack of synchronism, substantially increased power would be required to maintain system oscillation. With the feedback circuit to the invention, however, the transformer 27 provides an output signal at the new resonant frequency, and this, in turn, is amplified by the amplifier 36 and applied to the valve 18, so as to assure application of the driving power at the resonant frequency of the system.

Although the invention has been described herein with respect to a specific embodiment, many modifications and variations therein will readily occur to those skilled in the art. For example, if a feedback loop gain greater than unity is maintained at all times, the start generator 35 may be omitted and oscillation of the system may be initiated by inserting a transient signal into the amplifier 36. Accordingly, all such variations and modifications are included within the intended scope of the invention, as defined by the following claims.

We claim:

1. Resonating apparatus comprising a member supported for oscillatory motion, spring means linked to the member to permit oscillation at a resonant frequency dependent upon the characteristics of the member and the spring means, oscillatory drive means for maintaining oscillation of the member, electrical detector means including a first element movable with the member and a second element in relatively fixed position and in electrically cooperative relation with the first element for detecting changes in the frequency of oscillation of the member and producing a corresponding electrical signal, and electrical control means responsive to the signal from detector means for controlling the operation of the oscillatory drive means to maintain synchronism between the drive means and the member.

2. Resonating apparatus according to claim 1 wherein the control means includes phase shifter means for adjusting the phase of the signal from the detector means to compensate for phase variations between the signal from the detector and the oscillatory drive means.

3. Resonating apparatus according to claim 1 wherein the oscillatory drive means comprises hydraulic piston and cylinder means and the control means includes servo valve means for supplying hydraulic fluid to the piston and cylinder means in accordance with signals derived from the detector means.

4. Resonating apparatus according to claim 1 wherein the detector means comprises linear velocity differential transformer means having a core element which is movable in accordance with oscillatory motion of the member.

5. Resonating apparatus comprising a member having a resonant frequency, drive means for oscillating the member, detector means for detecting the frequency of oscillation of the member and control means responsive to the detector means for controlling the operation of the drive means to maintain synchronism between the drive means and the member, wherein the control means includes self-excited electrical oscillator means responsive to signals derived from the detector means for producing a corresponding output signal and summing amplifier means responsive to signals from the detector means and from the electrical oscillator means to produce an output signal of sufficient magnitude to maintain oscillation of the member under low gain conditions.

6. Resonating apparatus comprising a member supported for oscillatory motion, spring means linked to the member to permit oscillation at a resonant frequency dependent upon the characteristics of the member and the spring means, oscillatory drive means for maintaining oscillation of the member, detector means for detecting the frequency of oscillation of the member, and control means responsive to the detector means for controlling the operation of the oscillatory drive means to maintain synchronism between the drive means and the member wherein the control means includes self-excited electrical oscillator means responsive to signals derived from the detector means for producing a corresponding output signal and summing amplifier means responsive to signals from the detector means and from the electrical oscillator means to produce an output signal of sufficient magnitude to maintain oscillation of the member under low gain conditions.

7. Resonating apparatus according to claim 5 including gain control means for adjusting the gain of the summing amplifier means to control the amplitude of oscillation of the member and wherein the output of the electrical oscillator means is dependent upon the setting of the gain control means.

8. Resonating apparatus according to claim 1 including a second member linked to the spring means for oscillation in opposed phase relation to the first mentioned member.

9. Resonating apparatus according to claim 1 including resilient support means supporting the member from a base While permitting oscillatory motion in a direction perpendicular to the direction between the member and the base.

10. Resonating apparatus according to claim 1 wherein the member includes an array of grinding tubes extending perpendicularly to the direction of oscillation thereof, and including means for supplying fluid material to the array of grinding tubes during oscillation of the m ber,

References Cited UNITED STATES PATENTS LESTER M. SWINGLE, Primary Examiner D. G. KELLY, Assistant Examiner U.S. Cl. X.R. 

